Impression Materials

Making an imprint

Impression and Cast

Impression: -ve replica of the oral hard and soft tissues

Cast: +ve replica of the oral hard and soft tissuesDie: Metal cast or any cast for single tooth

Impression TraysContainer used to carry the impression material into or out from the patient’s mouth

Stock trays Special trays

Under cutAreas under the inclined planes

X

Ideal requirements of Impression materials

Biologically Non- toxic and non-irritant

InterfaciallyCompatible with different model and die materials

Chemically 1. Have long shelf life2. Dimensionally stable in storage Stable in storage

Ideal requirements of Impression materials

Mechanically 1. When set they should behave elastically

2. Have sufficient mechanical properties ie. tear strength to resist tearing during impression removal from the undercuts

3. Have sufficient flow under pressure that helps in recording the fine details of the oral structure

Practicability1. Inexpensive

2. Easy manipulated

3. Have reasonable working and setting times

Classification of Impression Materials

I. According to the mechanical behavior

A. Elastic materialsUsed for both edentulous and dentate patients having undercuts

1. Hydrocolloids Reversible hydrocolloid (Agar) Irreversible hydrocolloid (Alginate)2. Elastomeric Materials Polysulfide Silicones (Condensation-polymerizing & addition-

polymerizing) Polyether3. Gutta Percha

I. According to the mechanical behavior

B. Inelastic (Rigid) materials Used only with edentulous patients having no or shallow under cuts

1. Plaster of Paris2. Impression compound3. Zinc oxide Pastes4. Impression waxes

Classification of Impression Materials

II. According to the setting mechanism

A. Chemically-set materialsBecause of the irreversible reaction, they are used only for one time

1. Plaster of Paris2. Zinc oxide pastes3. Alginate hydrocolloid4. Elastomeric materials

Classification of Impression materials

II. According to the setting mechanism

B. Physically-set materialsBecause of the reversible reaction they are able to be reused

1. Impression compound2. Agar hydrocolloid3. Impression waxes4. Gutta percha

Classification of Impression materials

III. According to the usage

A. Materials for making 1ry impressionUsed in stock trays, thick consistency, record poor details

1. Impression compound (Complete denture)

2. Alginate hydrocolloid (Removable and fixed prosthesis)

3. Putty and heavy consistencies of rubber impression materials

(Removable and fixed prosthesis)

Classification of Impression materials

III. According to the usage

B. Materials for making 2ry impressionUsed in special trays, thin consistency, record fine details

1. Plaster of Paris (Complete denture)2. Zinc oxide pastes (Complete denture)3. Impression waxes (Complete denture)4. Agar hydrocolloid

(Removable and fixed prosthesis)5. Medium and light consistencies of

rubber impression materials(Removable and fixed prosthesis)

Classification of Impression materials

RIGID IMPRESSION RIGID IMPRESSION MATERIALSMATERIALS

1.Impression plaster

2. Impression compound

3. Zinc oxide pastes

Manipulation of these materials will be handled in the lab classes

1. IMPRESSION PLASTER1. IMPRESSION PLASTER

It is a rigid impression material, used in shellac special trays to make 2ry

impressions for edentulous patient has no or shallow undercuts.

It is one of the gypsum products that based on - Ca2 So4. ½ H2O (-calcium

sulfate hemihydrate)

PresentationPresentation

The material is presented as powder to be mixed with water to form a slurry

(soft creamy mix)

Composition of the powderComposition of the powder

-calcium sulfate hemihydrate….basic constitute

Potassium sulfate….anti expansion and accelerator

Borax……retarder Coloring agent…… Alizarine red

Flavoring agent….Ment Starch….Facilitate the removal of stone cast

-calcium sulfate hemihydrate

Setting reactionSetting reaction

The material sets via chemical reaction named crystallization

The reaction is characterized by heat generation and setting expansion

The reaction could be influenced by;

P/L ratio, Mixing rate (time and speed), Particle size, Temperature, Additives (Acc. &

Ret.)

The calcium sulfate hemihydrate gets some water and changes into inter-meashed calcium

sulfate dihydrate crystals

PropertiesProperties1. Biological properties Non toxic and non-irritant Cause dehydration to oral soft tissues

2. Interfacial properties Requires separating medium before pouring of

gypsum cast and die materials

3. Mechanical properties Rigid after setting and should not be used in

patients with sever undercuts

Brittle after setting and could be fractured in clean cut lines during impression removal from shallow undercuts (i.e. fractured parts could be assembled).

PropertiesProperties

4. Chemical properties Little degree of dimensional changes due to the

presence of anti-expansion additives.

Material’s powder should be stored in dry, tightly closed containers to elongate the shelf life

5. Practicability Easy manipulation Resenable setting time Somewhate short working time

2. IMPRESSION COMPOUND2. IMPRESSION COMPOUND It is a rigid thermoplastic impression material, used in stock trays to make 1ry

impressions for edentulous patient has no or shallow undercuts.

Types1. Low fusing (True impression material,

..…softening temp. 45-60oC)

1. High fusing (Tray compound,

….. softening temp. 70-130oC)

PresentationPresentation

L.F. Cakes for full impression H.F. Cakes for making special trays L.F. Green sticks for border tracing

L.F. Cones for copper ring impressions

CompositionComposition

Thermoplastic resins…

gives thermoplastic behavior Waxes…

Flow, stickiness, and give thermoplastic behavior Filler (Talc, chalk)…

consistency, stickiness Plasticizer (Stearic acid) …

moldability (plasticity) and facilitate the flow Coloring agent

Setting ReactionSetting Reaction

Thermoplastic material changes its Physical state by temperature change

On Heating ……Hard Soft

On Cooling ……Soft Hard

The material is bad thermal conductor, so sufficient heating is required for

homogenous softening. Sufficient cooling is also required for proper hardening

PropertiesProperties

1. Biological properties Non toxic and non-irritant Overheated material could burn the soft

tissue

2. Interfacial properties Does not require separating medium before

pouring the gypsum cast

3. Mechanical properties Rigid after cooling and should not be used in

patients with sever undercuts

PropertiesProperties

4. Chemical properties Thermoplastic material Little degree of dimensional changes due to

thermal change and release of stresses Overheating evaporates the plasticizer

Moldability

5. Practicability Easy manipulation, Reasonable W.&S. Times The material could be reused Impression should be disinfected before

pouring in gypsum and sterilized before reusing

2. ZINC OXIDE PASTES2. ZINC OXIDE PASTES It is a rigid impression material, used in

acrylic special trays with border tracing to make 2ry impressions for edentulous

patient has no or shallow undercuts.

Uses of Zinc oxide pasteUses of Zinc oxide paste1. Impression material

2. Bite registration

3. Surgical pack

TypesTypes1. ZOE paste..contains eugenol in its

formulation

2. Eugenol-free paste.. contains carboxylic acid derivative instead of eugenol

The eugenol-free material overcomes The eugenol-free material overcomes the drawbacks of the eugenol;the drawbacks of the eugenol;1. Eugenol taste could be unaccepted by some

patients

2. Eugenol could irritate the soft tissue

3. Leaching of the eugenol out of the material could cause gastric troubles

Both types are Both types are presented as presented as

two-paste systems two-paste systems

(Base and Catalyst)(Base and Catalyst)

Base Catalyst

ZOE white paste red paste

E-free white paste blue paste

PresentationPresentation

CompositionComposition

Base pasteCatalyst paste

1.Zinc oxide2.Oils (olive oils)

3.Resins4.Accelerator (Zinc acetate )

Eugenol- containing materials1.Eugenol (Oil of clove)2.Fillers (Kaoline, talc)

3.Accelerator (Zinc acetate)4.Moisture

Eugenol-free materials1. Carboxylic acid drevative [e.g. EBA]2. Ethyl alcohol as vehicle

Setting ReactionSetting Reaction

ZOE sets through chemical reaction named chelation

(1)….ZnO + H2O Zn(OH)2

(2)…. Zn(OH)2 + Eugenol (2HE) ZnE2 + H2O

The reaction could also be accelerated in presence of higher temperatures, little amount of moisture, 1ry

alcohol

Eugenol-free material sets through chemical reaction named saponification

ZnO + 2RCOOH (RCOO)2 Zn + H2O

PropertiesProperties

1. Biological properties Non toxic and non-irritant Eugenol could irritate the soft tissue

2. Interfacial properties Does not require separating medium

because of its oil content

3. Mechanical properties Rigid after setting and should not be used in

patients with sever undercuts

PropertiesProperties

4. Chemical properties Impression inaccuracy could result from the

warpage of acrylic trays Dimensionally stable on storage

5. Practicability Easy manipulation, Reasonable W.&S. Times Impression should be disinfected before

pouring in gypsum, however long term immersion could cause erosion of impression surface